An Uber car allegedly comes under attack in Paris, where cab drivers are on strike.

Uber, the service that allows you hail a car ride from your smartphone, has faced bureaucratic obstacles and legal challenges in nearly all of the cities where it has tried to expand, typically from local taxi and limousine commissions that aren't happy about the competition. Today in Paris, those paperwork protests turned into smashed windows and flat tires.

Five thousand French taxi drivers are on strike today, and in Paris, one of the world's great tourism cities, a system-wide cab shutdown could give cabbies lots of leverage. But with startup companies like Uber now operating, it is possible to get a ride—and striking drivers are angry. Multiple men allegedly attacked an Uber car carrying passengers away from the airport; those passengers included Kat Borlongan of the consulting firm Five by Five, who tweeted about the attack. Another of the occupants, tech CTO, said that striking drivers blockaded much of the roadway out of the airport, forcing cars to pass by them one by one, at which point they allegedly threw rocks at the Uber van.

Uber has been operating in France since December, when new rules allowed such phone-based services to pick up passengers as long as they wait 15 minutes. Paris taxi drivers aren't keen to see foreign-based competition expanding into their turf, and their strike demands include making Uber-like services wait at least half an hour before picking up passengers.